Wind box for a chemical recovery furnace

ABSTRACT

The present document describes a wind box used in the air supply of a chemical recovery furnace, the wind box comprising a frame ( 1 ) having at least one air inlet opening ( 2 ) and at least one air supply opening ( 3 ) through which air is led from an air channel via the wind box to the recovery furnace. The wind box further comprises at least one combined actuator ( 25 ) for regulating the air flow through the wind box and for cleaning each air supply opening ( 3 ) as well as means ( 19, 21 ) for moving each actuator ( 25 ). The invention is based on using a cleaning head ( 15 ) smaller than the air supply opening ( 3 ) when cleaning the air supply opening ( 3 ), whereby its path instead of a longitudinal motion is determined to be curved such that one to and from motion of the cleaning head will rub of all deposit from both the upper and the lower edge of the air supply opening ( 3 ) and also from the area between these.

The invention relates to a wind box comprising a frame having an airopening and means for cleaning the air opening and for controlling theair flow through the wind box. Such wind boxes are used in chemicalrecovery furnaces, such as the soda recovery boilers used in thecellulose industry, air being supplied into the furnace with the aid ofwind boxes in the case of such boilers.

Soda recovery boilers are used when producing chemical pulp by thesulphate process. Hereby the wood material is pulped in a cooking liquorcontaining sodium sulphide and sodium hydroxide, such liquor beingtermed white liquor. A residue from the pulping process is a liquorcalled black lye which contains residual chemicals and organic materialfrom the wood pulp. This black lye is concentrated and injected into thesoda recovery boiler where the organic material is combusted at a hightemperature. During combustion the chemicals contained in the black lyeaccumulate onto the bottom of the soda recovery boiler as a melt. Fromthe boiler bottom the melt is taken to further processing in order tocirculate the chemicals back into the pulping process. Excess thermalenergy is also released during combustion, which is then recovered in asteam power plant.

In order to achieve as complete a combustion as possible and a processhaving high efficiency, a large amount of air is needed in the process.This replacement air is taken to the boiler via the line of air openingsaround said boiler by blowing. The air is brought to the air openingsthrough an air channel surrounding the boiler via housings called windboxes. The air flow is also generally regulated by means of theequipment contained in these wind boxes.

A problem with soda recovery boilers is the accumulation of black lye asdeposit at the edges of the air openings. This accumulated deposit leadsto an uneven air flow and thus to a reduced efficiency of the combustionprocess. If the deposit is not removed sufficiently often and thoroughlyenough, it tends to form hard accumulations which are difficult toremove.

In accordance with the prior art, actuators cleaning the air openingsare arranged in the wind boxes in addition to air flow regulators. Suchactuators are described in, e.g. FI Patent Application No. 913132 and FIPatent Specification No. 74796. These solutions are characterized by acleaning blade smaller than the air opening, which blade moves in a backand forth motion and whose angle of impact and thereby the part of theair opening being cleaned is varied between the impact motions. Theproblem with such solutions is the very complex mechanism required forchanging the angle of impact, in addition to which a separate system forregulating the air flow is needed. Furthermore, it is usually impossibleto clean the edge areas of the centre part of the oval air openings withthis equipment, and in their rest position the cleaning heads usuallyunnecessarily restrict the air flow through the wind box.

Combined devices are also known which seek to simplify the constructionof the wind box by combining in one and the same device both functions,regulation of the air flow and cleaning of the air opening. One suchdevice is described in FI Patent Specification No. 62178. The operationof the device is based on a shaft which is inserted through the airopening and moves in the longitudinal direction and is furnished withwings at its end. The intention is to use these wings for cleaning theair opening and, by adjusting their angle, also for restricting the airflow. Even this solution is hampered by the complexity and the poorfunctionality of the construction. From FI Patent Specification No.87270, a simpler combined device is also known whose operation issimilarly based on a cleaning head fixed to a shaft moving along alongitudinal path. In this solution the cleaning end is adjusted suchthat it is nearly equal in size to the air opening, whereby the entireinner part of the air opening can be cleaned with one to-and-frommovement, but not, however, the so called beard accumulating around theouter edges of the air opening. A further problem hampering thissolution is that the large cleaning head easily gets stuck in the airopening, preventing the operation of the wind box.

The aim of the invention is to eliminate the drawbacks hampering theabove-described prior art and to provide a wind box containing anentirely novel type of combined device for regulating the air flow andfor cleaning the air opening.

The invention is based on that, instead of a longitudinal motion, thepath of the cleaning head, which is smaller than the air opening, isdetermined as being curved such that with one to-and-from motion, thecleaning head rubs off the deposit from both the upper and the loweredge of the air opening and also from the area between these.

The invention offers considerable benefits. The construction of thedevice is most simple, for in addition to the cleaning head and themeans for moving it, all that is needed is a fixed guide way whichdetermines the path of the cleaning head. The path of the cleaning headcan also be designed such that over some section of its path thecleaning head together with an air slide possibly connected theretooperates as a means for regulating the air flow. Thus, the deviceaccording to the invention combines the advantages of theabove-described prior-art devices in a novel, superior manner. Thedevice enables the cleaning of the so called beard accumulating at theupper and lower edge of the air opening as do devices with varyingimpact angles, and in addition it is also possible to clean the edgeareas of the entire air opening, as with the device which is furnishedwith a cleaning head the size of the air opening. In the wind boxaccording to the invention, the cleaning head can be pulled out of thetravel path of the air flow, and even manual cleaning is possible viathe conventional manual access port which remains free in the wind box.All in all, the invention makes it possible to achieve an excellentfunctionality of the air chamber simultaneously combining it withfacilities for regulating the air flow in the same device in a mostsimple and reliable manner.

In the following, the invention is described in more detail by means ofa number of examples and with reference to the annexed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a wind box according to theinvention.

FIG. 1A illustrates a detail of FIG. 1.

FIG. 2 depicts a group of wind boxes according to the invention.

The wind box comprises a metal frame 1 and parts connected theretoeither directly or via another part. The frame 1 is provided with an airinlet 2 and an air outlet 3, i.e. an air opening. The air inlet 2 isarranged at the upper part of the body 1 and is connected to an airsupply channel (not shown) via which hot (about 140° C.) air is suppliedto the wind box to be led further via the outlet 3 to the processchamber (not shown). The environment of the air inlet 2 and the outlet 3is provided with fixing means 4 and 5 which are used to fix the wind boxto the wall of the process chamber and to the system of air supplychannels, simultaneously sealing these connections. The free internalwidth of the wind box frame 1 is advantageously equal to the maximalwidth of the air opening 3, and correspondingly, the internal width ofthe frame 1 is slightly greater than the maximal height of the airopening 3.

The back of the wind box frame 1 is provided with a manual access port 7and a control port 11. The access port 7 makes it possible to clean theair opening even manually using a conventional sweeping method. Themanual access port 7 is closed by means of a closing flap 8 hinged tothe upper edge of the port 7, whereby a counterweight 9 is attached tothe flap 8. The purpose of the counterweight 9 is to press the closingflap 8 against the access port 7 and to close the port 7 when the port 7is not used for maintenance purposes. The control port 11 is an openingneeded when operating the cleaning and control mechanism of the airopening 3. In addition, a round opening 10 for monitoring is providedbetween the control port 11 and the manual access port 7, whereby aglass window can be arranged in the opening for monitoring in order toenable a visual examination of the operation of the wind box and the airopening 3.

A hanger 17 is mounted at the mouth of the control port 11 external ofthe frame, a cylinder support 18 being hinged to the hanger such thatthe support 18 is capable of turning e.g. about 30 degrees round itssupport point in the vertical direction. An air cylinder 19 is fixed tothe cylinder support 18 at its one end. The operation of the aircylinder 19 is controlled with normal control gear (not shown), wherebya shaft 20 fixed to the cylinder 19 piston can be pushed out of thecylinder 19 or pulled into the cylinder 19. A fixing device 6 isprovided at the end of the shaft 20 which remains outside of the aircylinder 19 for connecting the shaft 20 to an operating rod 21.

The operating rod 21 is a rod whose task it is to transmit the movementand force transmitted from the air cylinder 19 via the shaft 20 furtherto actuators inside the wind box.

The operating rod 21 extends from the fixing device 6 at the end of theshaft 20 to the cylinder support 18 and further via a hole in thesupport 18 and the control port 11 inside the wind box. The control port11 is furnished with a gasket 26 (FIG. 1A) of Teflon® which reduces theleaking of the pressurized air flowing inside the wind box out of thewind box and through which the operating rod 21 passes. The gasket isfitted in the control port 11 such that the rotating motion of thegasket and a change in the direction of the centre axis of the holethrough the gasket are possible.

A limiter frame 22 is mounted outside the control port 11, in thevicinity of the shaft 20 and the operating rod 21, essentially parallelwith the shaft 20 and the operating rod 21, the limiter frame consistingof two parallel, elongated metal plates mounted at a distance from oneanother by means of support blocks, the plates having several holes 23with matching positions. A spline or pin 24 limiting the movement of theshaft 20 out of the cylinder 19 and thereby also the movement of theoperating rod 21 from inside the wind box frame 1, can be insertedthrough these holes 23.

Two metal plates 12 and 13 have been welded inside the frame 1 of thewind box on its side walls. The plates 12 and 13 are designed andpositioned such that a gap of a certain shape in the longitudinaldirection and having a width of about 30 to 35 mm remains between them,the gap forming the guide way 14. An actuating system 25 is arranged onthe guide way 14, the actuating system 25 consisting of a cleaning head15, an air slide 16, four wheels 26 and means for fixing the wheels 26.At its end on the side of the air slide 16 the actuator 25 is connectedto the operating rod 21 by means of a joint which enables the actuator25 and the operating rod 21 to turn with respect to each other.

The wheels 26 of the actuator 25, whose diameter is a bit smaller thanthe gap between the metal plates 12 and 13, are fixed to the air slidemember 16 of the actuator 25, two at both edges of the slide 16. Thisconstruction makes it possible to move the actuator 25 back and forthalong the guide way 14 in the following manner: when the air cylinder 19is operated such that it pushes the shaft 20 out, the operating rod 21moves outwards from the wind box simultaneously pulling the actuator 25behind it along the guide way 14 and the actuator 25 thus follows thepath determined by the guide way 14. When the air cylinder 19 pulls theshaft 20 inwards, the operation of the wind box is reversed. It shouldbe noted that the hinged mounting of the air cylinder 19 to the frame 1of the wind box via its support 18 together with the turning gasket (notshown) of the control port 11 make a component deviating from thelongitudinal direction of the operating rod 21 possible for the movementof the actuator 25.

The shape of the guide way 14 is determined by the desired path of theactuator 25. In this embodiment the forward end of the guide way 14,this being the end which is situated farther away from the air opening3, is slightly upwards slanted in the forward direction of the guide way14 and is situated close to the upper edge of the wind box frame 1.Hereby both the air slide 16 and the cleaning head 15 are placed in theupper part of the wind box, where they do not disturb the air flowthrough the box. The shaft 20 of the air cylinder 19 is then pushed out.

When the pulling of the shaft 20 of the air cylinder 19 into the aircylinder is initiated, the actuator 25 enters the control area for theair flow. In this area the guide way 14 is slanted steeply downwardswhereby, when the actuator 25 progresses along the guide way 14, thecleaning head 15 is pressed down restricting the air flow, and at thesame time the air slide 16 closes the flow path of air over the cleaninghead 15. If desired, the air flow in the wind box can be restricted byplacing the spline 24 of the limiting frame 22 in a positioncorresponding to the desired air flow and by guiding the end of theoperating rod 21, more specifically the fixing device 6 of the shaft 20and the operating rod 21, against this spline 24 by means of the aircylinder 19.

When pushed forward on the guide way 14, the actuator 25 reaches thecleaning area. At the beginning of this area the guide way 14 isstraight and progresses obliquely downwards at an angle which in theembodiment shown in the drawings deviates from the horizontal plane byabout 35 to 40 degrees. In practical applications in general this anglemay be about 20 to 60 degrees from the horizontal plane. When theactuator 25 progresses over the straight part of the guide way 14 thetop of the cleaning head 15 approaches the lower edge of the air opening3, encountering it and finally passing the lower edge at a smalldistance either without touching it or lightly rubbing the lower edge.The shape of the cleaning head 15 is such that at the encountering anglein question the intersecting line of the lower edge of the cleaning head15 on the surface determined by the air opening 3 is essentially similarin shape to the lower edge of the air opening 3. Hereby the cleaninghead 15, when passing the lower edge of the air opening, effectivelyremoves deposits accumulated on this edge.

When the top of the cleaning head 15 has been pushed sufficiently far,typically 2 to 40 cm and in this embodiment about 10 to 20 cm, past theair opening 3, the actuator 25 reaches the steeply upward slantedsection of the guide way. Hereby the cleaning head 15 begins to turnobliquely upwards and during this turning the edges of the cleaning head15 rub off the deposit from the edges of the air opening 3. The endsection of the guide way 14 is directed almost vertically upwards whichmakes it possible to clean also the upper edge of the air opening 3during the same backward motion of the air cylinder 19. For cleaning thelower edge the cleaning head 15 usually protrudes about 2 to 40 cm pastthe upper edge of the air opening 3. In the embodiment depicted in thedrawings the cleaning head 15 passes the upper edge by about 10 to 20cm. The shape of the upper edge of the cleaning head 15 is also suchthat at the end point of the guide way 14 the intersectional line of theupper edge of the cleaning head 15 on the surface determined by the airopening 3 is essentially similar in shape to the upper edge of the airopening 3.

In this embodiment, the air opening 3 has roughly the shape of avertically elongated hexagon with rounded corners. The maximum width ofthe air opening 3 is about 100 mm and its maximum height is about 300mm. More generally, air openings 3 are typically elliptic or the like inshape and in more conventional installations they are rectangular inshape. The invention can be applied in connection with all these airopenings by dimensioning the wind box and its actuators to correspond tothe shape of opening in question.

The guide way 14 and the actuator 25 cleaning the air opening 3 andregulating the air flow in the wind box must be dimensioned such thatthe entire air opening 3 is cleaned. The width of the cleaning head 15is determined by the width of the air opening such that the former isslightly narrower than the latter. The shapes of the upper and loweredges of the cleaning head 15 are determined by the path of the cleaninghead 15 and the shape of the air opening 3 such that each sectional areaof the plane determined by the surface of the air opening 3 and thecleaning head 15, when the cleaning head 15 travels through its entireintended path, is a sub-area of the surface determined by the airopening 3. At the same time the combination of these sectional areas isas close as possible to the surface determined by the air opening 3. Inthe present embodiment the cross-section of the cleaning head 15essentially has the shape of a rhombus rounded at its upper and lowerends and standing on one end. The length of the cleaning head 15 is suchthat the cleaning head 15 can be inserted past the edges of the airopening 3 the above-described sufficient distances.

Also the other parts of the actuator 25 are dimensioned according toeach application. The width of the air slide 16 which is fixedlyconnected to the rear part of the cleaning head 15 is determined by thefree width of the inner part of the wind box frame 1 such that theformer width is slightly narrower, and its length is determined suchthat when the actuator 25 is in position to regulate the air flow, therear edge of the air slide 16 always extends close to the upper surfaceof the wind box frame 1. The wheels 26 are fixed to the air slide 16 toits both edges such that two wheels 26 are aligned with respect to oneanother and the other two are also aligned with respect to one anotherin the longitudinal direction of the air slide 16 at a distance of about5 to 15 cm from the first pair of wheels.

Even solutions differing from the above-described embodiments arefeasible within the scope of the invention.

The guide way 14 can also be implemented without wheels 26, for exampleby using slide rails. The way 14 can also be made from e.g. a bar alongwhich the air slide 16 and the cleaning head 15 move supported bybarrels. In wind boxes according to the invention the shape of the way14 may also differ from what is depicted in the drawings depending onthe application in question. Furthermore, it is possible to arrange theway 14 such that it is upside down compared to what is shown in thedrawings, whereby the actuator 25 is in its rest position at the lowerpart of the wind box, and first cleans the upper edge of the air opening3, then its centre part and finally its lower edge, as it moves alongits cleaning path. In principle, it is also possible to design the airslide 16 and the guide way 14 such that the guiding of the air flow iscarried out by controlling the air slide 16 such that it moves in frontof the air inlet port 2, thus narrowing the flow route.

The possible position of the guide way 14 in the wind box is not limitedonly by the side walls of the frame 1 but these provide an advantageousand a natural support base for the way 14. Furthermore, the constructionshown in the drawings is simple and functional, and in this constructionthe position of the guide way 14 does not constitute an obstaclelimiting the design of the path of the cleaning head 15 and the members16, 21 connected thereto.

Many variations are possible within the scope of the invention when theoperating rod 21 and the air cylinder 19 are positioned. It is notadvantageous in all possible embodiments for the control port of theoperating rod 21 to be arranged close to the upper part of the frame 1;instead, it may be arranged e.g. in the middle section in the verticaldirection of the frame 1. The air cylinder 19 can also be turned suchthat when the cylinder 19 pushes its shaft 20 outward, the end of theshaft 20 which is connected to the operating rod 21 moves toward thewind box and not away from it, as is the case in the embodiment depictedin the drawings. Hereby also the reverse action of the air cylinder 19,the pulling in of the shaft 20, is reversed as compared to the previousexamples.

It is also possible and in many applications preferred to use the sameair cylinder 19 to control several wind boxes. In the case of two windboxes this can be carried out as shown in FIG. 2, whereby the shaft 20of the air cylinder 19 guides a transverse beam 27 to which theoperating rods 21 of two adjacent wind boxes are connected. The aircylinder 19 can then be positioned in the space between the wind boxeswhereby the space required by the wind box system in the longitudinaldirection is reduced.

The wind box can also be constructed so wide that it comprises severalair openings 3. Hereby a cleaning head 15 is provided for each airopening 3, but the air slide 16 may advantageously also be shared. Allcleaning heads 15 of the wind box are simplest to control by means ofthe same air cylinder 19.

Restricting the path of the actuator 25 comprising an air slide 16 and acleaning head 15 has been described above. This was done by means of alimiting frame 22 and a spline or pin 24 which were employed tomechanically prevent the shaft 20 from protruding further out than hasbeen predetermined of the air cylinder 19, whereby the pulling of theoperating rod 21 from inside the frame 1 was also restricted. Acorresponding limiting operation can also be carried out by means ofmagnetic limit switches, whereby the magnetic limiters are arranged e.g.on the surface of the air cylinder 19. When the shaft 20 of the cylinder19 has protruded a distance corresponding to the position of thelimiter, the limit switch controls the actuators of the air cylinder 19such that the shaft 20 is locked in this position. In this embodiment ofthe wind box mechanical limiting devices 22 and 24 are not necessarilyneeded.

What is claimed is:
 1. A wind box intended for the air supply of achemical recovery furnace, comprising a frame (1) having at least oneair inlet opening (2) and at least one air supply opening (3) for takingair through the frame (1) to the recovery furnace, at least one at leastpartly curved guide way (14) which is connected to the frame, at leastone actuator (25) which is arranged to be movably supported against theguide way (14) for regulating the air flow through the frame (1) and forcleaning each air supply opening (3), and means (19, 21) connected tothe actuator (25) for moving the actuator (25) along the guide way (14),characterized in that each guide way (14) comprises both a sectioncurved in a first direction and a section curved in a second direction,and the actuator (25) is arranged to be supported against each guide way(14) at least two points deviating in the direction of the guide way(14), whereby the direction of the actuator (25) follows the directionof the guide way (14) when the actuator (25) is moved along the guideway (14).
 2. The wind box of claim 1, characterized in that forregulating the air flow through the wind box the guide way (14)comprises a section where the actuator (25), when stopped, is inside theframe (1) in front of the air supply opening (3) at least partiallycrosswise such that the path of air to the air supply opening (3) isrestricted.
 3. The wind box of claim 1, characterized in that both sidewalls of the frame (1) are provided with tracks or rails aligned withrespect to each other and forming the guide way (14), or fixed pieces(12, 13) between which two essentially uniformly broad slots alignedwith respect to each other form the guide way (14).
 4. The wind box ofclaim 1, characterized in that the guide way (14) has a section arrangedto guide the actuator (25) to the top part of the frame (1) in order toreduce the effect of the actuator (25) which restricts the air flow. 5.The wind box of claim 1, characterized in that the guide way (14) has asection which begins close to the lower part of the frame (1) and issteeply curved upwards, said section being situated in front of the airsupply opening (3) and arranged to control the cleaning head (15) suchthat it sets in a motion where the cleaning head (15) moves from thelower edge of the air supply opening (3) to its upper edge.
 6. The windbox of claim 1, characterized in that a rod (21) is hinged to the rearpart of the actuator (25), there is an opening (11) in the back wall ofthe frame (1), a gasket is fitted in the opening such that it can beturned, and the rod (21) is arranged to travel through the opening (11)and the gasket.
 7. The wind box of claim 6, characterized in that oneend of the rod (21) is fixed to an air cylinder (19) arranged to movethe actuator (25) via the transmission of the rod (21).
 8. The wind boxof claim 7, characterized in that, in order to restrict the movement ofthe cylinder (19) shaft (20) and the rod (21), the wind box comprises anelongated piece (22) which is essentially parallel to the air cylinder(19) and is provided with several holes (23) which are perpendicular tothe longitudinal direction of the cylinder (19), and a spline (24)arranged to be inserted into such holes (23).
 9. The wind box of claim7, characterized in that the rod (21) is connected to the air cylinder(19) via the transmission of a transversal beam (27) to which even thecorresponding rod (21) of another wind box is connected, in order tooperate more than one wind box using the same air cylinder (19).
 10. Thewind box of claim 1, characterized in that the actuator (25) comprises acleaning head (15) whose upper edge is essentially similar in shape tothe upper edge of the air supply opening (3), lower edge is essentiallysimilar in shape to the lower edge of the air supply opening (3), andmiddle part is essentially equal in width to the air supply opening (3).11. The wind box of claim 1, characterized in that the actuator (25)comprises a cleaning head (15), an air slide (16) fixedly connected tothe rear end of the cleaning head 15), and wheels (26) mounted on bothsides of the air slide (16), on which wheels the actuator (25) isarranged to move along the guide way (14).